character motivation (bad intent)

okay so I have a basic plot outline but my key issue is trying to come up with a convincing enough motive for y bad guy. it's sort of about power and control and knowledge/power through knowledge. can anyone give suggestions of what basic things I'll have to include in the bad guy's motive to be the bad guy?

You should of added a little more information about this character. The thing with evil, it's not hard to convince someone that someone is evil. Then again, it's a positive thing if your readers don't really know if he's bad or not, adds to the story, gives it suspense. Show the audience how evil he is. Everyone has a motive or goal, but to act on those goals is something different. Show him doing heinous shit. If the guy is torturing someone or killing someone, I don't think the audience will say: "What a good guy."

Depends if you're going for a sort of senseless, psychotic kind of bad or if they're doing the wrong thing for the right reason, morally grey scenario. Characters that are just evil, want to destroy stuff while rubbing their hands together and twiddling their moustache aren't much fun to write and not interesting to read. You might need to outline a bit more about the plot and how the character fits in.

Often great characters are both likable and despicable. This popular form of villain has given us Dexter Morgan and Tony Soprano to name just two. Conflicted characters or villains with charisma (say, Hans Gruber from Die Hard) are generally more interesting than catatonic serial killers.

yeah I would go for the memorable and terrible bad guy. Someone you can love to hate and even empathize with. That's the golden ticket to an antagonist. To figure out how to work that into your story we would need some more details, but hopefully that gives you some direction.

There is a trope that in the first few scenes you show the protagonist saving a puppy and the antagonist kicking a puppy. It happens in the opening scenes of many, many movies, but not literally with puppies. Kicking a puppy may be a boss telling an employee to work over Christmas or some guy recounting a tale of some racist or homophobic act with glee. Saving a puppy may be giving an employee a Christmas hamper or helping an old lady across the street. It is there to set up the characters in the minimum time and effort.

Another trope is that bad guys are paedophiles; basically as a writer you take the most heinous act you can think of and use it as shorthand for "this man is evil incarnate". These are tropes I would avoid as they tend to result in two-dimensional, cartoon antagonists.

Personally I prefer shades of grey, which is why motivation is important. But more details would be needed before I could provide any. The relationship between the protagonist/ antagonist. The conflict. The setting. A brief character outline in terms of personality, occupation, interests etc.